/*
 * @(#)JdbcWrapper.java
 *
 * @author	  Orlin Tomov
 * 
 */
package dbu.jdbc.facade;

import java.sql.SQLException;
import java.sql.Wrapper;


/**
 * Interface for JDBC classes which provide the ability to retrieve the delegate instance when the instance
 * in question is in fact a proxy class.
 * <p>
 * The wrapper pattern is employed by many JDBC driver implementations to provide extensions beyond
 * the traditional JDBC API that are specific to a data source. Developers may wish to gain access to
 * these resources that are wrapped (the delegates) as  proxy class instances representing the
 * the actual resources. This interface describes a standard mechanism to access 
 * these wrapped resources
 * represented by their proxy, to permit direct access to the resource delegates.
 * 
 * @since 1.6 
 */

abstract class JdbcWrapper implements Wrapper{

	/**
	 * Returns an object that implements the given interface to allow access to
	 * non-standard methods, or standard methods not exposed by the proxy.
	 * 
	 * If the receiver implements the interface then the result is the receiver 
	 * or a proxy for the receiver. If the receiver is a wrapper
	 * and the wrapped object implements the interface then the result is the
	 * wrapped object or a proxy for the wrapped object. Otherwise return the
	 * the result of calling <code>unwrap</code> recursively on the wrapped object 
	 * or a proxy for that result. If the receiver is not a
	 * wrapper and does not implement the interface, then an <code>SQLException</code> is thrown.
	 *
	 * @param iface A Class defining an interface that the result must implement.
	 * @return an object that implements the interface. May be a proxy for the actual implementing object.
	 * @throws java.sql.SQLException If no object found that implements the interface 
	 * @since 1.6
	 */
	@Override
	public <T> T unwrap(Class<T> iface) throws java.sql.SQLException {
		throw new SQLException("not supported");
	}

	/**
	 * Returns true if this either implements the interface argument or is directly or indirectly a wrapper
	 * for an object that does. Returns false otherwise. If this implements the interface then return true,
	 * else if this is a wrapper then return the result of recursively calling <code>isWrapperFor</code> on the wrapped
	 * object. If this does not implement the interface and is not a wrapper, return false.
	 * This method should be implemented as a low-cost operation compared to <code>unwrap</code> so that
	 * callers can use this method to avoid expensive <code>unwrap</code> calls that may fail. If this method
	 * returns true then calling <code>unwrap</code> with the same argument should succeed.
	 *
	 * @param iface a Class defining an interface.
	 * @return true if this implements the interface or directly or indirectly wraps an object that does.
	 * @throws java.sql.SQLException  if an error occurs while determining whether this is a wrapper
	 * for an object with the given interface.
	 * @since 1.6
	 */
	@Override
	public boolean isWrapperFor(Class<?> iface) throws java.sql.SQLException {
		throw new SQLException("not supported");
	}
}